P10-Lecture 19-Eukaryotes & Protists- March 26

P10-Lecture 19-Eukaryotes & Protists- March 26 -...

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Unformatted text preview: Origin of Eukaryotes & Multicellularity Origin of Eukaryotes Evolutionary Clock s Eukaryotes s Began 2.1 bya Evolutionary Clock s Eukaryotes s Began 2.1 bya Evolutionary Clock s Eukaryotes s Began 2.1 bya Evolutionary Clock s Eukaryotes s Began 2.1 bya Big Idea: Evolution is a tinkerer s 1) Pathways for production of ATP in aerobic respiration apparently borrowed from (or at least shared with) photosynthesis! s 2) Anaerobic origins of photosynthesis apparent even in modern plants x Enzymes used for fixing CO 2 are interfered with by O2 - photorespiration x s "Prokaryotes" oldest, most diverse group x All combinations of energy, carbon sources Summary s Early Earth environment anaerobic x Only anaerobic glycolysis possible - low yield x Very widespread, apparently old s Photosynthesis -> Oxygen revolution 2.5bya x Bad for anaerobes (major extinction!) x Allowed aerobic respiration! s Big Idea: Evolution as tinkering Eukaryotes s Took about 1.6 billion years for eukaryotes to arise x Remember - life arose in just a few hundred million years s Eukaryotes include x "Protists" - mostly unicellular x Plants, animals, fungi "Prokaryotes" vs. Eukaryotes (Briefly) s Unlike Eukaryotes, prokaryotes have x No nuclear envelope x No membrane bound organelles x Circular DNA, with relatively few genes Fig. 7.1, 7.6 Prokaryotes vs. Eukaryotes s Prokaryotes x Naked DNA x Circular genome x No membrane s Eukaryotes (Typically) x Nuclear membrane x Linear chromosomes x Mitochondria and, in bound organelles x Few membranes x No "sex" x "Flagella" some, Chloroplasts x Endomembranes x Sex, meiosis x 9+2 flagella "Protists" are ___?___phyletic s United by x being eukaryotic x lack of multicellularity 3 usually s Four issues today x Origin of eukaryotes x Eukaryote features x Brief overview of "protist" diversity x Rise of multicellularity See Fig. 29.1 Origin of Eukaryotes - Two theories s Not mutually exclusive s 1. Autogenous theory ancestral prokaryote x Some or all differences evolved from the See Fig. 29.10 Origin of Eukaryotes - Two theories s 2. Endosymbiosis Theory x Eukaryotes arose from one species living inside another! x E.g. chloroplasts, mitochondria x Mitochondria evolved first See Figure 29.11 Endosymbiosis Theory Lynn Margolis"Symbiosis is a major driving force behind evolution." "Life did not take over the globe by combat, but by networking." Evidence for Endosymbiosis s 1. Similar types of endosymbiosis x Protists inside each other - radiolarians x Protists inside animals - e.g. cows; termites Endosymbionts: Coral & Zoozanthellae Amoeba-Bacteria Symbiosis s Support to Margulis' theorys Kwang W. Jeon- Univ. Tenn.- 1991 x New bacterial symbionts became integrated in host amoeba Evidence for Endosymbiosis s 2. Size x Mitochondria/chloroplasts similar in size to prokaryotes. 3 0.02 micrometer (um) to 1um Evidence for Endosymbiosis s 3. Similar membranes x Prokaryotic membranes and membranes of mitochondria and chloroplasts have similar properties. - similar enzymes similar transport systems Evidence for Endosymbiosis s 4. Mode of replication x Mitochondria & chloroplasts reproduction is similar to binary fission of bacteria Evidence for Endosymbiosis s 5. Mitochondrial and chloroplast genome resembles prokaryote genome x Simple genome, with circular DNA 3 Unlike nuclear genome x No histones with DNA Evidence for Endosymbiosis s 6. Mitochondria and chloroplast transcription x Have their own ribosomes, etc. 3 Ribosomes more similar to prokaryotic ribosomes than eukaryotic x Susceptible to similar antibiotics x Coding sequences similar to bacteria! x Protein synthesis most like prokaryotes: 3 1st amino acid is like bacteria, not like eukaryotes The Tree of Life Phylogenetic support See Fig. 29.12 Secondary Endosymbiosis s A heterotrophic protist engulfed cyanobacteria containing plastids. x Eukaryote taking in another eukaryote See Fig. 29.16 Secondary Endosymbiosis s Many examples of secondary endosymbiosis with chloroplasts Fig. 29.17 Back to Metabolism: Endosymbiosis - Why do it? s Represents an extreme form of mutualism x Ancestral Mitochondrion 3 Aerobic Fig. 28.17d x Ancestral Prokaryote 3 Source of Carbon and protection x Ancestral Chloroplast 3 Energy 3 Source from light of Carbon x Ancestral Eukaryote and protection Eukaryote Features and History s Biomarkers 2.7 bya s Modern Eukaryotes have: x Membrane bound nucleus x Membrane bound organelles x Chromosomes x Cytoskeleton 3 Microtubules - Tubulin. Cilia, flagella 3 Microfilaments - Actin s Mitochondria Back to metabolism x From aerobic prokaryote x Allow aerobic metabolism x Efficient regeneration of ATP s Chloroplasts x From photosynthetic prokaryote x Allow harvesting of solar energy Evolution of Multicellularity s Has arisen many times, e.g. x Independently in plants, fungi, animals, kelp x In plants, fungi, animals has allowed extreme specialization of cells. 3 Protists must do everything in one cell Protists Nutritionally most diverse of all eukaryotes. Ecologically grouped: protozoans; photosynthetic (algal) and absorptive (fungus-like). Most are motile; aquatic Protists are Paraphyletic Coloniality s Many protists are colonial x E.g. Choanoflagellates, Volvox x Allows Division of labor among cells 3 Some Volvox cells specialized for reproduction- gametes Summary s Origin of Eukaryotes took a while x Prokaryotes/Eukaryotes very different s Eukaryote origins x Autogenous vs. Endosymbiotic theories x Chloroplasts, mitochondria from endosymb. s Protists Paraphyletic x Selected protist diversity s Coloniality common in Protists s Multicellularity has evolved many times ...
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